I have a 2009 Nissan frontier VQ40DE that is having difficulty starting after sitting for a while. FYI, this might be related to another p0171-2009-nissan-frontier-t630887.html issue I had previously. After it starts it seems to run okay. I looked at it in mode 6 and it has occasional misfire (1-5) on multiple cylinders. It's not throwing any codes. Will the truck throw a code if the fuel pressure is low?

Nissans in general have no pressure sensor on the lift pump, although all the ones with DGI have one on the high-pressure side. So the short answer is no, low fuel pressure won't throw any specific code. Minimum pressure should be 51 psi if you put a gauge on it, that's standard for the lift pump on pretty much everything. It's possible you have a bad check valve in the pump, the pressure should hang above 40 for quite awhile after the system primes. If it drops quickly then the check isn't checking. It's also possible the pump is weak and not spinning up from the 1.5 second priming pulse. The gauge will show that up immediately, the pressure should shoot up to 51+ instantly when it primes. If it climbs up slowly or doesn't reach minimum, then the pump is weak.